CODEWITHSUNDEEP
c#foreachiterationvariable-assignment
user1306322
user1306322

Reputation: 8721

How to modify a foreach iteration variable from within foreach loop?

When I try to do this...

Item[,] array = new Item[w, h];  // Two dimensional array of class Item, 
                                 //   w, h are unknown at compile time.
foreach(var item in array)
{
    item = new Item();
}

...I get Cannot assign to 'item' because it is a 'foreach iteration variable'.

Still, I'd like to do that.

The idea is to assign default Item class values to existing item.

Upvotes: 21

Views: 48693

Answers (4)

Joe Shanahan
Joe Shanahan

Reputation: 816

Not knowing the size isn't a problem:

for (int i = 0; i < twoDimArray.GetLength(0); i++)
{
    for (int j = 0; j < twoDimArray.GetLength(1); j++)
    {
        twoDimArray[i, j] = ...
    }
}

Upvotes: 6

Jon Skeet
Jon Skeet

Reputation: 1499870

Okay, now that we know your aim instead of how you were trying to achieve it, it's much easier to answer your question: you shouldn't be using a foreach loop. foreach is about reading items from a collection - not changing the contents of a collection. It's a good job that the C# compiler makes the iteration variable read-only, otherwise it would have let you change the value of the variable without that actually changing the collection. (There'd have to be more significant changes to allow changes to be reflected...)

I suspect you just want:

for (int i = 0; i < array.GetLength(0); i++)
{
    for (int j = 0; j < array.GetLength(1); j++)
    {
        array[i, j] = new Item();
    }
}

That's assuming it's a rectangular array (an Item[,]). If it's an Item[][] then it's an array of arrays, and you'd handle that slightly differently - quite possibly with a foreach for the outer iteration:

foreach (var subarray in array)
{
    for (int i = 0; i < subarray.Length; i++)
    {
        subarray[i] = new Item();
    }
}

Upvotes: 29

Adam Robinson
Adam Robinson

Reputation: 185593

It looks like you're trying to initialize the array. You can't do that this way. Instead, you need to loop through the array by index.

To initialize the elements of a given two-dimensional array, try this:

for (int d = 0; d < array.GetLength(0); d++)
{
    for (int i = 0; i < array.GetLength(1); i++)
    {
        array[d, i] = new Item();
    }
}

Upvotes: 2

Pompair
Pompair

Reputation: 7311

You can use normal for loop for that.

Upvotes: 1

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